This invention relates to means for detecting Vibrio parahaemolyticus, thermolable enterotoxin (LT)-producing strains of Escherichia coli, human thermostable enterotoxin (hereinafter, STh)- and/or porcine thermostable enterotoxin (hereinafter STp)- producing toxigenic strains of Escherichia coli, and Staphylococcus aureus in clinical examination, in particular testing in case of food poisoning, or in food inspection.
When the material to be tested is patient's vomit, feces, food, or wipe, a series of operations, namely enrichment culture, isolation culture and differential culture, are required for final identification of the pathogen or contaminant as Vibrio parahaemolyticus, if present. The time periods required for the respective culture steps are 10-16 hours for enrichment culture, 18-24 hours for isolation culture, and 18-24 hours for differential culture, the total time being as long as 2-4 days. Tests to be included in differential culture include growth test in agar medium supplemented with NaCl, gram staining, oxydase test and so forth. They involve complicated and troublesome procedures and are time-consuming and expensive.
For detecting the pathogenic factor of Vibrio parahaemolyticus, the so-called reverse passive hemagglutination reaction is available which uses a specific immune globulin obtained from an antiserum to thermostable (thermostable) direct hemolysin (TDH) produced by Vibrio parahaemolyticus. However, this reaction needs 20-24 hours until a result is obtained.
As mentioned above, the prior art methods invariably need a very complicated procedure and a long period of time until identification as Vibrio parahaemolyticus, hence not suited for use in clinical laboratory testing, among others, which demands speediness.
Recently, the DNA probe or hybridization techniques, which use olgonucleotides, have been attempted. However, these techniques, which comprises hybridization with oligonucleotide label-modified probes on a membrane or some other support, followed by detection, can scarcely have a satisfactory detection sensitivity and selectivity.
Moreover, strains of Vibrio parahaemolyticus that have a novel pathogenic factor, namely TDH-related hemolysin (TRH), which is different from those so far reported, has been discovered recently and, further, it has become clear that the gene coding for TRH includes two types, namely trh1 and trh2, which differ in base sequence from each other. However, any method has been established as yet for directly testing for Vibrio parahaemolyticus strains having this new pathogenic factor.
For identifying a pathogen or contaminant as a toxigenic strain of Escherichia coli, enrichment culture, isolation culture, pure culture and confirmation culture are required and are to be followed further by serological testing, enterotoxin production test and other biochemical tests. Each culture step requires 18-24 hours and the total time, inclusive of the time for subsequent tests, amounts to as long as a week or so.
For detecting thermolabile enterotoxin (hereinafter, LT), kits for detecting enterotoxin which ultilize the reverse passive latex agglutination reaction are commercially available. However, since, immunologically, cholera enterotoxin (hereinafter, CT) and LT have common antigenicity, it is difficult to detect in distinction from each other.
Moreover, the samples should be pure cultures already roughly estimated with respect to their identification. The steps preceding and including this rough estimation step require complicated procedures and a long period of time. In addition, the time for working with said kits alone amounts to 20-24 hours.
As mentioned above, the prior art methods for detecting toxinogenic strains of Escherichia coli invariably need very complicated procedures and are time-consuming, hence are not suited for use in clinical laboratory testing, among others, which demands speediness.
Recently, the DNA probe or hybridization techniques, which use olgonucleotides, have been attempted. However, these techniques, which comprises hybridization with oligonucleotide label-modified probes on a membrane or some other support, followed by detection, can scarcely have a satisfactory detection sensitivity and selectivity.
For detecting and identifying STh- or STp-producing toxigenic strains of Escherichia coli, it is necessary to perform enrichment culture, isolation culture, pure culture and confirmation culture. Furthermore, a pathogen or contaminant can be identified as a thermostable enterotoxin-producing strain of Escherichia coli only after serologic, biochemical, and enterotoxin production tests.
However, 18-24 hours is required for each culture step, and the total time, inclusive of the time for the subsequent tests, amounts to at least one week.
The suckling mouse technique is the only testing method for the production of thermostable enterotoxin. For this method, mice 2-3 days after birth must be prepared and the procedure is complicated and requires skill. Moreover, three or more mice should be subjected to the test to obtain the mean value. For these and other reasons, said method is unsatisfactory in reproducibility and reliability.
Recently, the DNA probe or hybridization techniques, which use olgonucleotides, have been attempted. However, these techniques, which comprises hybridization with oligonucleotide label-modified probes on a membrane or some other support, followed by detection, can scarcely have a satisfactory detection sensitivity and selectivity.
The materials to be tested in case of food poisoning include patients' vomits, feces, the same foods as taken by patients and/or wipes used in patients' environment. For the detection and identification of Staphylococcus aureus in these materials, it is necessary to first perform enrichment culture, isolation culture, pure culture and confirmation culture.
However, 18-24 hours is required for each culture step, and the total time, including the time necessary for the subsequent tests, is very long, amounting to about 4 days.
Biochemical tests to be carried out following confirmation culture include, among others tests for aerobic growth, VP reactivity, nitrite reduction, Tween 80 hydrolysis, hyaluronidase activity, sugar degradation and so forth. These tests require complicated procedures and are time-consuming and expensive.
In the case of Staphylococcus aureus, testing of isolates for enterotoxin production is regarded as the most reliable method of identifying pathogenic bacteria causative of food poisoning and diarrhea. However, even when commercially available simple reagent kits are used, 18-20 hours is required until results can be obtained. This means lack of speediness. A simple reagent kit for enterotoxin E (see) is not commercially available.
Recently, the DNA probe or hybridization techniques, which use olgonucleotides, have been attempted. However, these techniques, which comprises hybridization with oligonucleotide label-modified probes on a membrane or some other support, followed by detection, can scarcely have a satisfactory detection sensitivity and selectivity.